Scale the deltaX/deltaY on the mouse wheel events to be consistent with the compositor implementati…

third_party/WebKit/LayoutTests/fast/events/scroll-in-scaled-page-with-overflow-hidden.html

 <style>
     html, body { margin:0; overflow: hidden; }
 </style>
 <script src="../../resources/js-test.js"></script>
 
 <div>
   This tests that a usually overflow: hidden viewport should be scrollable when
   scaled. Otherwise, you can't get to content you would have been able to get to
   had you not been zoomed it.
 </div>
@@ skipping 16 matching lines @@
 
         window.internals.setPageScaleFactor(2);
 
         // Note that with ScrollTopLeftInterop enabled, document.scrollingElement is
         // null because document.body is potentially scrollable (with overflow:hidden
         // the  box can still be scrolled programmatically).
         shouldBe("internals.visualViewportScrollY()", "0");
 
         if (window.eventSender) {
             eventSender.mouseMoveTo(100, 100);
-            eventSender.mouseScrollBy(0, -5);
+            eventSender.mouseScrollBy(0, -10);
         }
 
         shouldBecomeEqual("internals.visualViewportScrollY()", "200", finishJSTest);
     })();
 </script>